problem with TMV (thermo Mixing Valve)

[Markhales8]

I have recently installed a TMV in my bathroom and it has been very tempramental with the Hot water. If i turn the temp down then cold comes through no problem. if i turn it up to provide controlled ho****er then tap stops. If i'm lucky then i will get nice hot water. so i know the thermo bit works, its just not consistant. If i leave it for some time then return to it, then nothing comes out. I have even got to the point of sucking the water through the tap (creating a vacum) and then it works. I have currently removed the TMV and hot water comes through fine (bit hot). help. Not sure if i have just bought a cheap and nasty TMV.

 

[diamondgas]

Or a faulty one? :welcome: to the forum 🙂

 

[AWheating]

what hot water system do you have?

 

[Mike Jackson]

Could be a pressure issue. Most TMV issues I have come across are due to unbalanced pressures.

 

[mountainman]

Could be a pressure issue. Most TMV issues I have come across are due to unbalanced pressures.

Very true!

 

[Markhales8]

all. thank you for you responses. How would i check to see if the pressure is suitable? I would like to check this out before i look at buying a new one. Are there any good TMVs or TMVs that can deal with an imbalance in the water presure.

 

[aqualogic7]

The installation instructions will tell you if it will operate with unbalanced supplies also just check the valve is the right way round as this can cause the problems you are having

 

[Ray Stafford]

all. thank you for you responses. How would i check to see if the pressure is suitable? I would like to check this out before i look at buying a new one. Are there any good TMVs or TMVs that can deal with an imbalance in the water presure.

I think this is what AWHeating was getting at when he asked what sort of hot water system you have.

For example, if your cold is mains fed, and your hot is tank fed, then there will be a significant pressure difference on each side of the TMV.

The scale of the pressure difference depends on a) how high the mains pressure is, which often varies over time, and b) the difference in height between the tank feeding the cylinder and the outlet.

 

[Mike Jackson]

I have yet to find one that will cope well with unbalanced supplies. I used to get this problem a lot in care homes and always carried pressure reducing valves with me to bung on the cold supply. A lot of valves state that they are suitable for high or low pressure which a lot of people read as high and low pressure and think they will cope.

 

[nysk2008]

why did you fit one, just out of curiousity

 

[AWheating]

I think this is what AWHeating was getting at when he asked what sort of hot water system you have.

For example, if your cold is mains fed, and your hot is tank fed, then there will be a significant pressure difference on each side of the TMV.

The scale of the pressure difference depends on a) how high the mains pressure is, which often varies over time, and b) the difference in height between the tank feeding the cylinder and the outlet.

you read me like a book LOL 🙂

shame the question has still not been answered?

 

[AWheating]

most tmv valves will not work with an inbalanced supply between the hot and cold of more than 0.5-1 bar dependant on actual pressures. for example peglar tmv valves have a max pressure ratio of 5:1 from what i can remember.
there is one brand that does make valves thats designed to work with inbalanced supplys but i cant remember the name.